A comparison of serum and EDTA plasma in the measurement of glutamic acid decarboxylase autoantibodies (GADA) and autoantibodies to islet antigen-2 (IA-2A) using the RSR radioimmunoassay (RIA) and enzyme linked immunosorbent assay (ELISA) kits.
BACKGROUND
Glutamic acid decarboxylase antibodies (GADA) and tyrosine phosphatase antibodies (islet antigen-2 antibodies; IA-2A) are used in clinical practise to identify type 1 diabetes.


METHODS
GADA and IA-2A were measured with RSR-ELISA kits in samples from 76 newly diagnosed type 1 diabetic children and 120 healthy controls. The aim was to evaluate performance of RSR-ELISA kits for GADA and IA-2A when serum and Ca2+ treated plasma were used.


RESULTS
GADA achieved high area under the curve (AUC) both for serum 0.95 (95% CI 0.90-0.99) and for Ca2+ treated plasma 0.95 (95% CI 0.91-0.99). At specificity 98%, sensitivity was 84% for serum and 87% for Ca2+ treated plasma. IA-2A achieved AUC 0.92 (95% CI 0.87-0.97) for serum and 0.94 (95% CI 0.90-0.98) for Ca2+ treated plasma. Using the lowest standard (15 WHO-Units/ml) as cut-off, specificity for serum was 100% and for Ca2+ treated plasma 99% with sensitivity 74% in both cases. Sensitivity was higher in ELISA compared to RIA (74%; p = 0.0080) for GADA measurement and similar for ELISA and RIA IA-2A measurements (76%; p = 0.50).


CONCLUSIONS
Both RSR-ELISAs, GADA and IA-2A showed excellent performance for serum as well as for Ca2+ treated plasma.
Rahmati
Kobra
K
Unit for Diabetes and Celiac Disease, Wallenberg Laboratory, University Hospital MAS, Malmö, Sweden.
Lernmark
Ake
A
Becker
Charlotte
C
Foltyn-Zadura
Anna
A
Larsson
Karin
K
Ivarsson
Sten-Anders
SA
Törn
Carina
C
D000293:Adolescent; D019540:Area Under Curve; D001323:Autoantibodies / Q000097:blood*; D001324:Autoantigens / Q000276:immunology*; D002648:Child; D002675:Child, Preschool; D003922:Diabetes Mellitus, Type 1 / Q000097:blood; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods*; D005260:Female; D005968:Glutamate Decarboxylase / Q000276:immunology*; D006801:Humans; D008297:Male; D010949:Plasma; D011863:Radioimmunoassay / Q000379:methods*; D011933:Reagent Kits, Diagnostic; D054635:Receptor-Like Protein Tyrosine Phosphatases, Class 8 / Q000276:immunology*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D044967:Serum
D001323:Autoantibodies; D001324:Autoantigens; D011933:Reagent Kits, Diagnostic; D054635:Receptor-Like Protein Tyrosine Phosphatases, Class 8; D005968:Glutamate Decarboxylase